|  | 1.4 | Network Layer Functions
| 1.4.7 | ARP
To communicate on an Ethernet network, the source station must know the destination station's IP and MAC addresses. When the source has determined the IP address for the destination, the source's Internet Protocol looks into its ARP table to locate the MAC address for the destination. If the Internet Protocol locates a mapping of destination IP address to destination MAC address in its table, it binds the IP address with the MAC address and uses them to encapsulate the data. The data packet is then sent out over the networking media to be picked up by the destination. If the MAC address is not known, the source must send out an ARP request. To determine a destination address for a datagram, the ARP table on the router is checked. If the address is not in the table, ARP sends a broadcast looking for the destination station. Every station on the network receives the broadcast. The term local ARP is used when both the requesting host and the destination host share the same medium, or wire. Prior to issuing the ARP, the subnet mask was consulted. The mask determined that the nodes are on the same subnet.